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United States Patent |
5,019,283
|
Beltzer
,   et al.
|
May 28, 1991
|
Enhancing antiwear and friction reducing capability of certain xanthate
containing molybdenum sulfide compounds
Abstract
It now has been discovered that lubricating compositions containing an
additive formed by reacting Mo(CO).sub.6 with dixanthogen can be enhanced
by the inclusion in the composition ligands selected from polydentate
ligands and mixtures thereof. Thus, the present invention comprises a
major amount of an aoil of lubricating viscosity and a minor but effective
amount of an additive formed by reacting Mo(CO).sub.6 with dixanthogen of
the formula (ROCS.sub.2).sub.2 wherein R is an organo group having a
sufficient number of carbon atoms to render the additive soluble in the
oil; and a polydentate ligand or mixtures thereof, the mole ratio of
additive to ligand being in the range of from about 1:1 to about 1:4.
Inventors:
|
Beltzer; Morton (Westfield, NJ);
Habeeb; Jacob J. (Westfield, NJ);
Francis; James N. (Maplewood, NJ);
Colle; Karla S. (Houston, TX)
|
Assignee:
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Exxon Research and Engineering Company (Florham Park, NJ)
|
Appl. No.:
|
404141 |
Filed:
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September 7, 1989 |
Current U.S. Class: |
508/267; 508/272; 508/279 |
Intern'l Class: |
C10M 135/14; C10M 141/06 |
Field of Search: |
252/25,49.7,46.3,46.4,33.6,42.7
|
References Cited
U.S. Patent Documents
2951040 | Aug., 1960 | Hugel | 252/33.
|
3419589 | Dec., 1968 | Larson | 252/33.
|
3840463 | Oct., 1974 | Froesehmann | 252/42.
|
Primary Examiner: Howard; Jacqueline V.
Attorney, Agent or Firm: Dvorak; Joseph J.
Claims
What is claimed is:
1. A method of enhancing the antiwear and friction reducing properties of a
lubricating oil composition comprising an oil of lubricating viscosity and
a molybedenum and xanthate containing additive formed by reacting
Mo(CO).sub.6 with a dixanthogen of the formula (ROCS.sub.2).sub.2 wherein
R is an organo group having a sufficient number of carbon atoms to render
the additive soluble in the oil, the method comprising: adding to said oil
composition a polydentate ligand or mixtures thereof.
2. The method of claim 1 wherein the mole ratio of additive to ligand is in
the range of from about 1:1 to about 1:4.
3. The method of claim 2 wherein R is selected from alkyl, aralkyl and
alkoxyalkyl groups having from about 2 to about 20 carbon atoms, the mole
ratio of dixanthogen to Mo(CO).sub.6 is from about 1.5:1 to about 2:1.
4. The method of claim 3 wherein the polydentate ligand is a nitrogen
containing heterocyclic compound in which nitrogen is the hetero atom.
5. The method of claim 4 wherein the ligand is a dithiodipyridine.
6. A method of enhancing the antiwear and friction reducing properties of a
lubricating composition comprising an oil of lubricating viscosity and an
additive having the formula Mo.sub.4 S.sub.4 (S.sub.2 C-OR).sub.6 wherein
R is selected from organo groups having sufficient number of carbon atoms
to render the additive soluble in oil, the method comprising: adding to
the lubricating composition a ligand selected from polydentate ligands of
nitrogen containing heterocyclic compounds, the mole ratio of additive to
ligand being in the range of from about 1:1 to about 1:4.
7. The method of claim 6 wherein R is selected from alkyl, aralkyl and
alkoxyalkyl groups having from about 2 to about 20 carbon atoms, the mole
ration of dixanthogen to Mo(CO).sub.6 is from about 1.5:1 to about 2:1.
8. A method for improving a lubricating composition comprising an oil
selected from natural and synthetic oils of lubricating viscosity and an
additive composition formed by contacting Mo(CO).sub.6 and a dixanthogen
of the formula (ROCS.sub.2).sub.2 in the ratio of about 1.5:1 to 2:1 at
temperatures in the range of from about ambient room temperature to about
140.degree. C. for about 2 to about 10 hours, wherein R in the dixanthogen
is selected from alkyl, aralkyl and alkoxyalkyl groups having from about 2
to 20 carbon atoms, the method comprising: adding to the composition a
ligand selected from nitrogen containing heterocyclic polydentate ligands
or mixtures thereof in which the nitrogen is the hetero atom, the ratio of
ligand or mixture of ligands to additive being about 1:1 to about 1:4.
9. The method of claim 8 wherein the ligand is dithiodipyridine.
Description
FIELD OF THE INVENTION
The present invention is concerned with improved lubricating compositions.
More particularly, the present invention relates to lubricating
compositions having xanthate containing molybdenum sulfide compounds as
antiwear and antifriction additives. Indeed, this invention is concerned
with enhancing the antiwear and friction reducing capability of such
molybdenum compounds by including in the composition polydentate ligands.
BACKGROUND OF THE INVENTION
Molybdenum disulfide is a well-known lubricant additive. Because it is
insoluble in lubricating oils, however, oil soluble sulfur containing
molybdenum compounds have been proposed and investigated as lubricant
additives. For example, in U.S. Pat. No. 2,951,040, an oil soluble
molybdenum xanthate is disclosed as being useful in lubricating
compositions. Apparently, the molybdic xanthate decomposes under
conditions of use to form an oil insoluble solid molybdenum sulfide on the
metal surfaces being lubricated.
U.S. Pat. No. 3,419,589 discloses the use of certain "sulfurized"
molybdenum (IV) dialkyldithiocarbamates as lubricant additives. These
additives are described as being oil soluble or at least capable of being
easily suspended in oils.
U.S. Pat. No. 3,840,463 discloses the use of certain metal
dialkyldithiocarbamates or dithiophosphates in combination with metal-free
additives containing sulfur and phosphorus.
U.S. Pat. No. 4,588,829 discloses the use of (disulfido) tris (N,
N-substituted dithiocarbamato) Mo(V) complexes in lubricant compositions.
In copending application Ser. No. 404,142, filed Sept. 7, 1989, there is
disclosed a multifunctional additive formed by reacting molybdenum
hexacarbonyl with dixanthogens of the formula (ROCS.sub.2).sub.2 wherein R
is an organo group having a sufficient number of carbon atoms to render
the additive soluble in a base lubricating oil.
SUMMARY OF THE INVENTION
It now has been discovered that lubricating compositions containing an
additive formed by reacting Mo(CO).sub.6 with dixanthogen can be enhanced
by the inclusion in the composition ligands selected from polydentate
ligands and mixtures thereof. Thus, the present invention comprises a
major amount of an oil of lubricating viscosity and a minor but effective
amount of an additive formed by reacting Mo(CO).sub.6 with dixanthogen of
the formula (ROCS.sub.2).sub.2 wherein R is an organo group having a
sufficient number of carbon atoms to render the additive soluble in the
oil; and a polydentate ligand or mixtures thereof, the mole ratio of
additive to ligand being in the range of from about 1:1 to about 1:4.
This and other aspects of the present invention will be readily appreciated
after reference to the Detailed Description, which follows.
DETAILED DESCRIPTION OF THE INVENTION
The lubricant compositions of the present invention include a major amount
of oil of lubricating viscosity. This oil may be selected from naturally
occurring mineral oils or from synthetic oils. The oils may range in
viscosity from light distillate mineral oils to heavy lubricating oils,
such as gas engine oil, mineral lubricating oil, passenger car oils and
heavy duty diesel oils. In general, the viscosity of the oil will range
from about 5 to about 26 centistokes at 100.degree. C. and especially in
the range of 10 to 18 centistokes.
The lubricant composition of the present invention includes a minor but
effective amount of an additive formed by reacting molybdenum
hexacarbonyl, Mo(CO).sub.6, with dixanthogen, (ROCS.sub.2).sub.2. The
reaction is conducted at temperatures ranging from about ambient room
temperature to about 140.C and preferably at temperatures of about
80.degree. C. to about 120.degree. C. For example, the Mo(CO).sub.6 and
the dixanthogen may be refluxed in toluene for times ranging from about 2
to about 8 hours.
The reaction time and temperature will depend upon the dixanthogen selected
and the solvent used for carrying out the reaction.
Useful solvents for carrying out the reaction include aromatic
hydrocarbons, especially toluene.
Suffice it to say that the reaction is conducted for a time sufficient to
form the additive.
Dixanthogens especially useful in the practice of the present invention can
be represented by the formula (ROCS.sub.2).sub.2 in which R can be the
same or different organo groups selected from alkyl, aralkyl and
alkoxyalkyl groups having a sufficient number of carbon atoms to render
the additive that is formed soluble in a lubricating oil. Preferably, R
will have from 2 to 20 carbon atoms. Indeed, it is particularly preferred
that R is an alkyl group having from 2 to 20 carbon atoms, and especially
from 4 to 12 carbon atoms.
In forming the additive of the present invention, the mole ratio of
dixanthogen to molybdenum hexacarbonyl should be greater than about 1.5 to
1. For example, in preparing the additive, it is preferred to use mole
ratios of (ROCS.sub.2).sub.2 to Mo(CO).sub.6 in the range of from about
1.6:1 to about 2:1.
Depending primarily upon the time and temperature at Which the Mo(CO).sub.6
and (ROCS.sub.2).sub.2 are reacted, the molybdenum and sulfur containing
additive that forms is a brown compound, a purple compound or a mixture of
both. Shorter reaction times, e.g., four hours or less, favor the
formation of the purple compound. Longer reaction times, e.g., four hours
or more, favor formation of the brown compound. For example, when (C.sub.8
H.sub.17 OCS.sub.2).sub.2 is reacted with Mo(CO).sub.6 in toluene for four
hours at 100.degree. C. to 110.degree. C., most of the starting material
is converted to the purple compound, with virtually none of the brown
being present. Continued heating of the reaction mixture results in
conversion of the purple compound to the brown compound; indeed, after
about six or seven hours, the purple form is largely converted to the
brown.
In general, it is preferred to contact the Mo(CO).sub.6 and dixanthogen for
a time sufficient for reaction to occur, but generally less than about 7
hours. Beyond 7 hours, undesirable solids begin to form. In order to
maximize the formation of additive and minimize formation of undesirably
solid by-products, it is preferred to react the Mo(CO).sub.6 and
dixanthogen at temperatures of about 100.degree. C. to about 120.degree.
C. for times ranging from about five to six hours, thereby producing
reaction mixtures which contain both the brown and purple additives of
this invention. This is no disadvantage because both forms are effective
lubrication additives, and mixtures of the two species (brown and purple)
perform as well as either species by itself.
The additives formed with R groups between about C.sub.4 H.sub.9 and about
C.sub.14 H.sub.29 can be readily separated from oily organic by-products
of the reaction by extracting the oily by-products with moderately polar
solvents as acetone, ethyl alcohol, or iso-propyl alcohol. The additives
with these R groups are substantially insoluble in such solvents, while
the oily by-products are soluble. Separation of the additives from the
by-products, however, is not necessary because the by-products do not
detract from the beneficial functional properties of the additives.
The physical properties of the purple and brown additives vary with the R
group. For example, the additive is crystalline solid when R is C.sub.2
H.sub.5 and the additive is an amorphous solid when R is larger than about
C.sub.7 H.sub.15.
The purple compound formed in reacting Mo(CO.sub.6) with (ROCS.sub.2).sub.2
is a thiocubane of the formula Mo.sub.4 S.sub.4 (ROCS.sub.2).sub.6.
The brown compound formed in reacting Mo(CO.sub.6) with (ROCS.sub.2).sub.2
is also believed to have a structure very similar to the thiocubane
structure of the purple compound based on its ease of formation from the
purple compound and chemical analysis.
The above described molybdenum-containing compounds are effective as
additives in lubricating compositions when they are used in amounts
ranging from about 0.01 to about 2.0 of weight percent, based on the
weight of lubricating oil, and preferably at concentrations ranging from
about 0.1 to about 1.0 weight percent.
Importantly, the lubricating composition of the present invention includes
a polydentate ligand or mixtures hereof. Those skilled in the art know
that the term "ligand" is used to designate functional coordinating groups
which have one or more pairs of electrons available for the formation of
coordinate bonds. Monodentate ligands can form only one bond with a metal
ion, while polydentate ligands can form more than one bond with a metal
ion. Polydentate ligands have been found to enhance the antiwear and
friction reducing properties of the product obtained from Mo(CO).sub.6 and
dixanthogens outlined above. Useful polydentate ligands include
heterocyclic compounds in which nitrogen is the hetero atom like triazole,
and dithiodipyridine. Particularly useful ligands in the practice of the
present invention are nitrogen containing polydentate ligands having
disulfide bonds like dithiodipyridine and thiadiazoles. Indeed,
dithiodithiodipy dipyridine is most preferred.
In the practice of the present invention, the mole ratio of molybdenum
containing additive to ligand will be in the range of from about 1:1 to
about 1:4 and preferably in the range of from about 1:1 to about 1:2.
If desired, other known lubricant additives can be used for blending in
lubricant compositions of this invention. These include ashless
dispersants, viscosity improvers and the like. These can be combined in
proportions known in the art.
The compositions of the present invention possess both antiwear properties
and antifriction properties.
The invention will be more fully understood by reference to the following
examples illustrating various modifications of the invention which should
not be construed as limiting the claims herein.
EXAMPLE 1
This example illustrates the preparation of a purple molybdenum and
xanthate containing additive for use in lube compositions according to the
present invention.
A mixture of 717 grams (1.75 moles) of octyl dixanthogen, (C.sub.8 H.sub.17
OCS.sub.2).sub.2, 263 grams (1 mole) of molybdenum hexacarbonyl,
Mo(CO).sub.6, and two liters of toluene was heated to 100.degree. C. with
stirring sufficient to agitate the heavy Mo(CO)6 crystals, which did not
completely dissolve. The temperature was gradually raised to 110.degree.
C. (refluxing the toluene) over a period of five hours, during which time
6 moles (about 150 liters) of carbon monoxide were liberated. The solution
turned purple, and all the Mo(CO).sub.6 dissolved. The toluene was removed
under a stream of nitrogen while maintaining the temperature of the
solution below 800.degree. C. A purple oil solidifying at about room
temperature was obtained which was extracted twice with 10 times the
volume of isopropyl alcohol containing 10% acetone. The alcohol insoluble
solid was separated by filtration, washed with ten times its weight of
cold hexane and then dried.
______________________________________
Elemental Analysis
% Mo % S % C % H
______________________________________
Found 22.49 29.42 37.26
6.09
Calc'd for 22.04 29.39 37.20
5.86
Mo.sub.4 S.sub.4 (C.sub.8 H.sub.17 OCS.sub.2).sub.6
______________________________________
X-ray structural analysis showed the product to be a thiocubane, Mo.sub.4
S.sub.4 (C.sub.8 H.sub.17 OCS.sub.2).sub.2.
A chromatogram of the product was obtained as follows. A small spot of the
sample was placed on a 2.times.6 cm piece of a commercially available
silica gel chromatography medium. It was developed with a mixture of 30%
toluene and 70% heptane. A dark purple spot at a retention factor (RF) of
about 0.6 was observed, and a very faint brown spot remained near the
origin.
EXAMPLE 2
This example illustrates the preparation of a brown molybdenum and xanthate
containing additive suitable in lube compositions of the present
invention.
The procedure of Example 1 was carried out, except that the reaction
mixture was heated for a total of 7 hours. At the end of the heating time,
the reaction mixture was allowed to cool to ambient temperature overnight.
The mixture was filtered to remove any insoluble material formed, and the
toluene removed and the brown residue was extracted as in Example 1. A
thin layer chromatogram of the brown solid was obtained. The chromatogram,
as in Example 1, showed little or no purple spot at a retention factor of
0.6, but a large dark brown spot near the origin.
Elemental analysis also was obtained with the results shown below.
______________________________________
Elemental Analysis
% Mo % S % C % H
______________________________________
Found 26.23 31.91 34.38
5.61
______________________________________
EXAMPLE 3
This example illustrates the preparation of a mixed additive useful in
compositions of the present invention.
The procedure of Example 1 was carried out, except that the reaction
mixture was heated for a total of 6 hours. The toluene was removed as in
Example 1 to yield a brownish-purple oil that partially solidifies upon
standing at room temperature for some time. Chromatography as in Example 1
reveals the presence of both a purple spot at RF 0.6, and a brown spot
near the origin. Exposure of the developed chromatogram to iodine vapors
formed an orange-brown spot at RF 0.75 due to the organic by-products of
the reaction mixture.
EXAMPLES 4 and 5
In these examples, lubricating compositions of the invention were evaluated
for wear protection using the Four Ball Wear Test procedure (ASTM Test
D2266). In all these tests, the base oil used was Solvent 150 Neutral. In
all instances, the additive used was Mo4S4(ROCS.sub.2).sub.6 wherein R is
an octyl group. In one run, zinc dialkyldithiophosphate was present. The
ligand used was 4,4' dithiodipyridine, designated as DTDP in Table I. The
compositions tested and the results are set forth in Table I.
TABLE I
______________________________________
Wear Volume in
Wt % mm.sup.3 .times. 10.sup.4 at
Mo.sub.4 S.sub.4
Wt % Wt % 100.degree. C., 1200 rpm
Run (ROCS.sub.2).sub.6
DTDP ZDDP 60 kg Load, 1 Hr.
______________________________________
1. Example 4
0.1 0.02 0.0 10
2. Example 5
0.1 0.04 0.0 10
3. Comp. Ex. 6
0.0 0.0 0.0 464
4. Comp. Ex. 7
0.1 0.0 0.0 210
5. Comp. Ex. 8
0.1 0.0 0.04 188
______________________________________
COMPARATIVE EXAMPLES 6 to 8
The Four Ball Wear Test was repeated using Solvent 150 Neutral (Comp. Ex.
6), Solvent 150 Neutral and the multifunctional additive Mo.sub.4 S.sub.4
(ROCS.sub.2).sub.6 (Comp. Ex. 7), and Solvent 150 Neutral with ZDDP (Comp.
Ex. 8). The results are also shown in Table I.
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